This invention relates to distributors with built-in crank angle sensors utilized in controllers of internal combustion engines such as automotive engines, and more particularly to distributors with built-in crank angle sensors which are enhanced in resistance against adverse effects of noises and which are small-sized and reduced in production cost and
Controller devices for automotive engines, etc., generally include: a crank angle sensor for generating reference signals corresponding to the reference crank positions of the respective cylinders of the engine, and a distributor for distributing a high ignition voltage to respective cylinders. The crank angle sensor and the distributor are usually attached to the same rotation shaft of the engine such that they form a single distributor unit with a built-in crank angle sensor.
FIG. 1 shows an axial section of a conventional distributor with a built-in crank angle sensor.
In FIG. 1, a rotation shaft 1 operatively coupled to the crank shaft of the engine is rotatably supported by a bearing 2. An electrode plate 3 electrically insulated from the rotation shaft 1 is disposed thereabove. A voltage source electrode 4 is in contact with the inner end of the electrode plate 3 to supply a high voltage. Discharge electrodes 5 for respective cylinders oppose the outer end of the electrode plate 3.
A rotation disk 6 has slits formed therethrough corresponding to the crank reference angular positions. A crank angle sensor unit 7 opposes the slits of the rotation disk 6. An electromagnetic shield cover 8 protects the crank angle sensor unit 7 from electromagnetic noises. An electrostatic shield cover 9 protects the crank angle sensor unit 7 from electrostatic noises.
FIG. 2 is an enlarged sectional view of the crank angle sensor unit of FIG. 1. A light emitting diode 11 and a photoreceptive element, namely a photodiode 12, opposes each other via the rotation disk 6. A hybrid integrated circuit 13 having a monolithic integrated circuit 13a forming part of the circuit thereof is coupled via a lead 14 to the photodiode 12. The output signal of the hybrid integrated circuit 13 is outputted via a lead 15 to the exterior circuit.
FIG. 3 is a circuit diagram of the hybrid integrated circuit of FIG. 2. Between a DC power source 21 and the light emitting diode 11 is inserted a resistor 22 for driving the light emitting diode 11. Another resistor 23 is inserted across the DC power source 21 and the photodiode 12. The light emitting diode 11 is coupled across the resistor 22 and the ground in the forward polarity.
A pull-up resistor 24 pulls up the output voltage V.sub.o of the hybrid integrated circuit 13. A constant voltage circuit, namely a Zener diode 25, is coupled across the DC power source 21 and the ground via the resistor 23. A load resistor 26 is inserted across the anode of the photodiode 12 and the ground. A capacitor 27 for suppressing the noises is coupled in parallel with the load resistor 26. A comparator 28 compares the voltage V.sub.D at the junction between the photodiode 12 and the load resistor 26 with the reference voltage V.sub.g. The cathode of the photodiode 12 is coupled to the cathode of the Zener diode 25. The load resistor 26 and the comparator 28 constitute a waveform shaper circuit for shaping the photoreceptive signal of the photodiode 12 into a rectangular waveform.
The operation of the conventional distributor with a built-in crank angle sensor of FIGS. 1 through 3 is as follows.
Together with the rotation shaft 1, the electrode plate 3 rotates with its inner end contacting the bottom end of the voltage source electrode 4. Thus, the outer end of the electrode plate 3 successively opposes the discharge electrodes 5 for the respective cylinders. Discharge is thus successively generated across the electrode plate 3 and the discharge electrodes 5, and the high ignition voltage is distributed to the respective cylinders.
The light emitting diode 11 is supplied from the DC power source 21 and emits light. The photodiode 12 opposing the light emitting diode 11 via the slits of the rotation disk 6 thus generates a photoreceptive signal which rises and falls at the front and the rear end of the slits, respectively. The hybrid integrated circuit 13 shapes the waveform of the photorecptive signal of the 12 into an output V.sub.o of rectangular waveform, which is supplied to the exterior circuits. Namely, the comparator 28 compares the voltage V.sub.D at the terminal of the load resistor 26 with the reference voltage V.sub.R, and thus shapes the photoreceptive signal of the photodiode 12 into an output signal V.sub.o of rectangular waveform.
Thus, the ignition plugs of the respective cylinders are supplied with the high ignition voltage via the discharge electrodes 5 of the distributor. The ignition timings are controlled by the output signal V.sub.o of the hybrid integrated circuit 13.
In the case of the above distributor, the distance from the photodiode 12 to the hybrid integrated circuit 13 is long. Thus, noises are prone to be superposed on the photoreceptive signal. The electromagnetic shield cover 8 made of a magnetic material and an electrically grounded electrostatic shield cover 9 are disposed for the purpose of preventing the noises. Namely, when a discharge is generated across the inner end of the electrode plate 3 and the discharge electrodes 5, electromagnetic noises are generated and superposed on the photoreceptive signal of the photodiode 12. The electromagnetic shield cover 8 prevents these noises. Further, although usually grounded, the rotation shaft 1 may be disconnected from the ground while rotating. Under such circumstances, a high voltage of the distributor is induced on the rotation shaft 1. Thus, the high voltage of the rotation shaft 1 is superposed on the photoreceptive signal as the electrostatic noises. The electrostatic shield cover 9 prevents these noises.
However, the photoreceptive signal of the photodiode 12 is weak. Further, the connection of the photodiode 12 with the load resistor 26 disposed on the hybrid integrated circuit 13 is effected via the lead 14, which exhibits a substantial area compared with the electrical connection pattern on the integrated circuit. Thus, noises are extremely prone to be superposed on the photoreceptive signal, and it is difficult to prevent these noises completely. If the input voltage V.sub.D to the hybrid integrated circuit 13 exceeds the reference voltage V.sub.R due to the superposed noises, the comparator 28 functions erroneously. The reliability of the ignition control is thus reduced.
Further, since the resistance to noises of the crank angle sensor unit 7 is small, the distance between the distributor portion and the crank angle sensor unit 7 cannot be reduced without adverse effects. This presents an impediment to the reduction of the size of the distributor as a whole.